Disaster Recovery Challenges

In this section we investigate some common challenges of DR in cloud environments.


Dependency

One of the disadvantages of cloud services is that customers do not have control of the system and their data. Data backup is on premises of service providers as well. This issue makes dependency on CSPs for customers (such as organizations) and also loss of data because of disaster will be a concern for customers. Dependency also creates another challenge which is the selection of a trusted service provider.

Figure 2. ENDEAVOUR flowchart


Cost

It is obvious that one of the main factors to choose cloud as a DR service is its lower price. So, cloud service providers always seek cheaper ways to provide recovery mechanisms by minimizing different types of cost. The yearly cost of DR systems can be divided in three categories:

  • Initializing cost: amortized annual cost
  • Ongoing cost: storage cost, data transfer cost and processing cost
  • Cost of potential disaster
  • Cost of recovered disasters and also cost of unrecoverable disasters.


Failure Detection

Failure detection time strongly affects on the system downtime, so it is critical to detect and report a failure as soon as possible for a fast and correct DR. On the other hand, in multiple backup sites there is a major question: How to distinguish between network failure and service disruption.


Security

As mentioned before, DR can be created by nature or can be human-made. Cyber-terrorism attack is one of human-made disasters which can be accomplished for many reasons. In this case, protection and recovery of important data will be a main goal in DR plans beside of system restoration.


Replication Latency

DR mechanisms rely on replication technique to make backups. Current replication techniques are classified into two categories: synchronous and asynchronous. However, both of them have some benefits and some flaws. Synchronized replication, guarantees very good RPO and RTO, but it is expensive and also can affect on system performance because of large overhead. This issue is more serious in multi-tier web applications, because it can significantly increase Round Trip Time (RRR) between primary and backup site. On the other hand, a backup model adopted with async replication is cheaper and also system suffers low overhead, but the quality of DR service will be decreased. Therefore, trading off between cost, performance of the system and also replication latency is an undeniable challenge in cloud disaster solutions.


Data Storage

Business database storage is one of the problems of enterprises which can be solved by cloud services. By increasing of cloud usage in business and market, enterprises need to storage huge amount of data on cloud-based storages. Instead of conventional data storage devices, cloud storage service can save money and is also more flexible. The architecture of a cloud storage system includes four layers: physical storage, infrastructure management, application interface and access layer. In order to satisfy applications and also to guarantee the security of data, computing has to be distributed but storage has to be centralized. Therefore, storage single point of failure and data loss are critical challenges to store data in cloud service providers.


Lack of Redundancy

When a disaster happens, primary site becomes unavailable and secondary site has to be activated. In this case, there is no ability to sync or async replication in a backup site but data and system states only can be stored locally. It is a serious threat to the system. This issue is temporary and will be removed after recovery of the primary site. However, to achieve the best DR solutions, especially in high availability services (such as business data storage), it is better to consider all risky situations.